The present invention pertains to the compounding of rubber. More particularly this invention pertains to compounds of vulcanizable rubber wherein a vulcanizing agent for the rubber is contained in a polymeric carrier which is substantially inert to cross-linking effects of the agent, and whereupon milling the compound the rubber and the polymeric carrier become blended, and the vulcanizing agent thus becomes distributed throughout the rubber for effecting the cure thereof.
It is known to mix rubber with compounding ingredients such as fillers and oils, and sometimes also one or more curatives such as activators or accelerators, in order to produce rubber masterbatches. A central theme in the masterbatching concept is that the product can be shipped to a purchaser in a remote location who can in turn use the compound with resort to little or no further addition and mixing of ingredients. If, however, a vulcanizing agent is added to the masterbatch at the time of original compounding, shelf-life comes into play, since the rubber begins to vulcanize during storage, and even though the rate of cure of the compound may be relatively slow at storage conditions, the state of cure can develop to an extent which renders the compound unprocessable if the storage life is too prolonged. In other words, the compound can no longer be processed by milling or extrusion, or otherwise further compounded or shaped into articles which can be subsequently vulcanized to set the shape of the articles and provide a desired combination of rubber stress-strain properties.